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Hannes Bester

Inverter mppt conversion

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Good evening all. 

I would like to ask something on behalf of a friend. This might sound very crazy but here goes. 

He has a small 1kva 12v inverter with a maximum mppt rating og 15-18v vdc and 600w. So he opted to get an external pwm which will allow a bigger pv array. He currently has 2 x 200w 28.6v panels but due to the 12v system he's battery discharge is high and the panels charging through the pwm can't keep up with the battery discharge current. So the question is would it be possible to open the inverter and locate the mppt output terminals and then connect the external pwm battery output to the internal mppt output to battery terminal to basically replace the function of the mppt if this is possible he would be able to set the inverter output source to SBU to use the power from the pwm instead of drawing from the battery?? I know this might sound very stupid but I thought I would rather ask the experts to give him an opinion. 

Thanks, have a good evening. 

Kind regards 

 

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2 minutes ago, Hannes Bester said:

Good evening all. 

I would like to ask something on behalf of a friend. This might sound very crazy but here goes. 

He has a small 1kva 12v inverter with a maximum mppt rating og 15-18v vdc and 600w. So he opted to get an external pwm which will allow a bigger pv array. He currently has 2 x 200w 28.6v panels but due to the 12v system he's battery discharge is high and the panels charging through the pwm can't keep up with the battery discharge current. So the question is would it be possible to open the inverter and locate the mppt output terminals and then connect the external pwm battery output to the internal mppt output to battery terminal to basically replace the function of the mppt if this is possible he would be able to set the inverter output source to SBU to use the power from the pwm instead of drawing from the battery?? I know this might sound very stupid but I thought I would rather ask the experts to give him an opinion. 

Thanks, have a good evening. 

Kind regards 

 

I have actually realized a potential problem with he's idea, if the pwm isn't connected to the battery it would not detect the operating voltage of the battery. 🙄

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Posted (edited)
6 hours ago, Hannes Bester said:

would it be possible to open the inverter and locate the mppt output terminals and then connect the external pwm battery output to the internal mppt output to battery terminal to basically replace the function of the mppt

With the low panel voltage models, the output of the SCC (which in this case sounds like a PWM type, not MPPT) is the battery (directly after the fuse). So no need to open it up.

Edit: so you're better off connecting the external solar charge controller directly to the battery, or as close as possible. It needs the best estimate of the battery voltage.

Edited by Coulomb

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3 hours ago, Coulomb said:

With the low panel voltage models, the output of the SCC (which in this case sounds like a PWM type, not MPPT) is the battery (directly after the fuse). So no need to open it up.

Edit: so you're better off connecting the external solar charge controller directly to the battery, or as close as possible. It needs the best estimate of the battery voltage.

Hi thanks for the feedback. I suggested to him to add more panels to his external pwm for obvious warranty reasons. At the moment the battery discharges at 25A at a range of 300 to 350w and he is only getting 13.8A of charge through the pwm. So he basically needs to up his charge to run the day without draining the battery. 

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